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L. HAMBURGER AND 0. LE LY. In.

ELECTRIC INCANDESCENT LAMP APPLICATION FILED IAN-11.1917.

I Patented Sept. 30, 1919.

INVENTORS I WITNESS Q? By A ilorneys,

UNITED STATES PATENT OFFICE.

' nonnwnx riniummenn. AND max LELY, .13., or EIN'D-HOVEN, nnrnnnnanns.

C ELECTRIC INGANDESCENT LAMP.

I To all whom it ma concern:

Be it known that we, LODEWIJK HAM- BURGER and DIRK LELY, Jr., subjectsof the Queen of the Netherlands, residing at Eindhoven, Kingdom of theNetherlands, have invented new and useful Improvements in or Relating toElectric Incandescent Lamps; and We do herebydeclare the following to bea full, clear, and exact description of the same.

In many electric incandescent lamps, for instance, those having atungsten filament, the temperature to which the filament may be raisedunder high vacuum, is not limited by the melting point of the metal, butby its vapor pressure,'because under such conditions of temperature andvacuum the Va porized metal condenses upon the bulb and obscures it. Ithas been proposed to prevent this obscuring of the bulb by introducingsubstances into the lamp which durin its burning evolved gases whichreacted with the vaporized or atomized particles of the filament, toform compositions which do not obscure the light as much as thecondensed filament vapors. In the case of tungsten filament lamps thismay be ef-' fected, for instance, by halogen or oxygen compounds. Theaforesaid substances have been placed in the lamp in locations ofgreater or less heat in accordance with their volatility ordecomposability.

It has been found however that many substances which even at hightemperatures do not give off any reacting vapor, such as oXid of sodiumNa U, sodium phosphate Na PO the fiuorids of the metals'of the alkalineearths and silica, SiO nevertheless may have a beneficent influence uponthe duration of the useful life of the lamp. This has proven to be thecase and in like degree even when a lamp, containing said substancesonly upon the inner walls of the bulb, was burnt while being immersed inliquid air. Ihe same action, the retarding of the obscuring of the bulb,was also found when in lieu of a tungsten filament, filaments of otherelements, for instance, carbon, molybdenum, platinum, iron, silver, zincor copper were used in the lamp. It follows clearly from these and otherexperiments that in the said cases the action cannot be ascribed to anyactive vapor, but only to the action of the introduced sub:

\ stance in a solid state. The present invention is based upon thisconclusion.

Specification of Letters Patent.

Application filed January 11, 1917. Serial ii'o. 141,840.

- to the invention Patented Sept. 30,1919.

The action of the solid substances upon the atomized particles from theincandescent Wire striking their surface is probably due primarily tothe formation of a solid (colloidal) solution in the solid layer. Ap-

plicants however do not wish to bind themselves to this explanation. Afavorable action of such substances is best realized When they areapplied to the incandescent lamp in such a place that they are struck bythe particles e ected from the wire. Preferably therefore the surface ofthe substance in the bulb should be large. When however the stablesubstance is placed in a glass tube or the like, genids which dissociate'by heat, it cannot act because the articles ejected from the wire willnot stri ie it. a

It is known that even small quantities of Water have a detrimentaleffect in 'a tungsten filament lamp. Therefore it is advantageous tochoose non-hygroscopic sub.- stances, because smaller precautions arethen necessary. As all soluble substances must be consideredhygroscopic, it is preferablev to use substances which are insoluble inwater.

In practice it has proven difficult to employ halogen or oxygendelivering substances in incandescent lamps burning under a high voltageof about 200 volts or higher, because arcing readily takes place betweenthe feed wires. In the. process according however no active vaporpressure is necessary, but on the contrary would have a deleteriouseffect, especially in high voltage lamps, because it furthers arcing.Therefore it is preferable to use only slightly volatile and highlystable substances.

So for example calcium fluorid CaF which is only slightly volatile andwhich is known to have a large degree of stability even at thetemperature of the electric arc, is especially fit for high voltagelamps. It has also the already mentioned advantage of being practicallyinsoluble in water, in consequence of which this substance has notendency to retain water or to absorb water from a moist atmosphere.

An embodiment of the invention is illus trated in the accompanyingdrawing wherein a conventional type of electric lamp with the bulb insection, is shown. a designates the filament supported in suitablemanner within the glass bulb b. On the inner walls as has been proposedfor haloits of bulb b is a coating 0 of the substance, as calciumfluorid, which is used to counteract the blackening of the bulb. Thethickness of the material 0 is shown much exaggerated in the drawing,this layer being in fact of little thickness and invisible.

It has been proposed (U. S. Patent No. 406,130) to coat the innersurface of carbon filament lamps with a thin film of a substance mixedwith more or less water, the substance being so chosen that the filmbecomes a good conductor of electricity, whereby the whole inner surfaceof the bulb is brought to the same potential as the filament in order toprevent the electrical carriage of material. The present invention,however, refers to an action obtained with a non-conducting film; allincandescent lamps in which a conducting film is applied upon thesurface of the globe, are expressly disclaimed.

It has been proposed (U. S. Patent No. 1,252,372) to coat the innersurface of the lamp bulb with a material, containing an oxidizing agent,which at the temperatures encountered under operating conditions, isable to combine with the dark deposit, the resulting material beingtransparent. In this case the temperature of the active material is muchhigher than the temperature of the bulbs of ordinary lamps of the vacuumtype, because the active material is put on a surface, working as aneconomizer that is reducing tie heat losses by the hot gases in agas-filled lamp. The present invention, however, refers to an action,obtained with a non-oxidizing substance, which does not reach atemperature hlgher than the bulb of an ordinary lamp of the vacuum type,all incandescent lamps in which an oxidizing agent is applied upon thesurface of the globe, being expressly disclaimed.

What we claim is:

1. An incandescent electric lamp of the vacuum type comprising a bulband a thin non-conducting layer on the inner surface of the bulb of anon-oxidizing substance which during the burning of the lamp does notevolve an active or measurable vapor pressure of an gas, but preventsthe obscuring of the ulb while solid.

2. An incandescent electric lamp of the vacuum type comprising a bulband a thin non-conducting layer on the inner surface of the bulb of anon-oxidizing substance which is practically insoluble in water andwhich during the burning of the lamp does not evolve an active ormeasurable vapor pressure of any gas but prevents the obscuring of thebulb while solid.

3. An incandescent electric lamp of the vacuum type comprising a bulband provided on the inner surface of the bulb with a thin layer offluorid of calcium.

In testimony whereof we have signed our names to this specification inthe presence of two subscribing witnesses.

LODEWIJK HAMBURGER. DIRK LELY, JUNIOR.

Witnesses:

J. J, HELSDON RIX, ANN NAG'I'IANZEE.

